1. Field of Invention
The present invention relates to a power-line-operated series-resonant inverter-type fluorescent lamp ballast wherein inversion frequency is automatically controlled such as to minimize deterioration of lamp current crest factor which would otherwise result from ripple on the inverter's DC supply voltage.
2. Elements of Prior Art
In conventional power-line-operated inverter-type fluorescent lamp ballasts, in order to attain a low crest factor of the lamp current, it is necessary to power the inverters from a DC supply voltage having little or no ripple.
Yet, in order for an ordinary rectifier arrangement to draw power from the power line with a relatively high power factor, it is necessary to permit the rectifier arrangement's output voltage to exhibit a relatively high degree of ripple.
Thus, in conventional power-line-operated inverter-type fluorescent lamp ballasts, there is a basic conflict between drawing power from the power line with a high power factor and at the same time providing a lamp current having a low crest factor.
To resolve this conflict, various forms of relatively complex power factor correction schemes are being used. These various power factor correction schemes function such as to cause power to be drawn from the power line with a relatively high power factor while at the same time providing a substantially constant-magnitude DC supply voltage.